Multilayer assembly with a central electrically conductive layer for use as an inductive sensor element

ABSTRACT

A multilayer assembly including a flexible, electrically conductive active central layer ( 532 ) with to main surfaces with a large area, i.e. a first surface adhered to at least one advantageously electrically insulating supporting layer ( 510 ) made of synthetic material and having substantially the same modulus of elasticity as the active central layer ( 532 ); and a second surface adhered to at least one advantageously electrically insulating second protective layer ( 520 ) made of synthetic material. The total thickness of the multilayer assembly is selected in such a way that the flexibility of the central adhesive layer ( 532 ) is substantially completely maintained. Said multilayer assembly may be used to treat or prevent bedsores.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT/FR97/01359 filed Jul. 22,1997 and a continuation of U.S. patent application Ser. No. 08/898,274filed on Jul. 22, 1997, now ABN.

The present invention essentially relates to a multi-layer producthaving an electrically conductive central layer that can be used as aninductive sensor element. More particularly, the invention relates to amulti-layer product including an electrically conductive central layerthat can be used as an inductive sensor element in the context of amethod and a device for improving support of a patient, in particularfor treating or preventing bedsores.

Documents U.S. Pat. Nos. 4,886,152; 4,009,312; 4,734,303; GB-A-2,103,999and GB-A-1,495,659 all relate to multi-layers metallic foils aspackaging materials.

Document EP-A-0 218 301 discloses a method and a device for improvingsupport of a patient, which support comprises a mattress provided withone or more closed chambers filled with a fluid under a controlledfilling pressure, and uses a measurement device based on a combinationof two induction coils 24, 25 shown in FIG. 4. That device is not verysatisfactory because it requires provision to be made to power bothinduction coils, i.e. including the moving induction coil which isdisposed close to the patient, and that always poses a safety problem.

In Document FR-A-2 718 347 =EP-A-676 158, which corresponds to U.S. Pat.No. 5,560,374, the applicant discloses a method and apparatus forsupporting an element to be supported, in particular the body of apatient, making it possible to support the element at an essentiallyconstant controlled penetration depth by means of a measurement devicecomprising an induction system combined with a piece of metal foilsituated under the body being supported. Displacement of the metal foilmodifies the self-induction coefficient of the induction coil, shiftingthe resonant frequency of the LC circuit away from the tuning frequencyof the oscillator, thereby damping the signal delivered to an amplifierby the oscillator, so as to ensure that the signal is correctlyprocessed and appropriately monitored.

It should be noted that the piece of metal foil situated under the bodybeing supported is generally arranged in the vicinity of that region ofthe element being supported which has the largest mass or which is mostprotuberant, generally the sacral region which constitutes the lowestposition of the element being supported, e.g. the body of a patient.

In the context of the applicant's prior solution, the metal foil issituated very close to the element being supported, e.g. a patient, andit suffers from the drawback of being noticeable to the element beingsupported.

Furthermore, the metal foil must not give rise to any adverse physicalphenomenon on the element being supported, especially when said elementis a patient. Likewise the metal foil must not disturb the treatment ofthe patient.

Therefore, a main object of the present invention is to solve the newtechnical problem consisting in providing a solution making it possibleto support an element to be supported, in particular the body of apatient, while using a measurement device for measuring the penetrationdepth to which the element being supported penetrates into the supportelement, without it being noticed by the element being supported, inparticular by a patient, and without giving rise to disturbances orphysical phenomena that might have adverse effects on the element beingsupported, in particular a patient, since any adverse effect on thetreatment of a patient is unacceptable.

Another main object of the present invention is to solve the newtechnical problem consisting in providing a solution making it possibleto support an element to be supported, such as the body of a patient,while using a measurement device for measuring the penetration depth towhich the element being supported penetrates into the support element,which measurement device is flexible enough to change shape to fit themorphology of the element being supported, in particular the morphologyof the body of a patient.

Yet another main object of the present invention is to solve the newtechnical problem consisting in providing a solution that makes itpossible to support an element to be supported while using a measurementdevice for measuring the penetration depth to which the element beingsupported penetrates into the support element, which measurement deviceuses a piece of metal foil designed so as to have very good flexibilityas well as very good mechanical strength, and in particular resistanceto degradation of its electrical characteristics.

All of these technical problems are solved for the first time by thepresent invention in a way that is simple, cheap, safe and reliable, andthat can be used on an industrial and medical scale.

In a first aspect, the present invention provides the use of amulti-layer film product, characterized in that it comprises anelectrically conductive flexible active central layer comprising twomain faces of large area, a first face glued onto at least one “support”layer of a synthetic material that is advantageously electricallyinsulating, and that has a coefficient of elasticity substantiallysimilar to that of the active central layer, and a second face gluedonto at least one “protective” second layer, in particular forprotecting against abrasion, and made of a synthetic material that isadvantageously electrically insulating, the total thickness of themulti-layer film product being chosen so that the flexibility of theactive central layer is retained substantially completely, as aninductive sensor element or in a measurement device for measuring thepenetration depth of an element being supported, in particular the bodyof a patient, which penetrates in a support device, for instance amattress or the like, preferably the protective layer being located infront of said element being supported, for instance the body of apatient. The invention also relates to a multi-layer film product aspreviously defined but wherein the active central layer is of a sizesmaller than the support layer and the protective layer. Therefore, thecentral layer does not have any edge liable to be apparent or in contactwith the outside. For instance, the size of the central layer is of theorder of 600 mm fold 600 mm and the size of the support layer is in theorder of 725 to 975 mm fold 1100 to 1400 mm and the size of theprotective layer is of the order of 700 mm fold 1000 mm.

In the context of the present description and of the claims, the term“flexible active central layer” indicates that the central layer has afolding flexibility in a direction perpendicular to the layer over itsmain faces of large area, thereby enabling it to change shape to fit themorphology of the element being supported, in particular the morphologyof the body of a patient. Likewise, in the present description and inthe claims, it is to be understood by the term “electrically conductiveactive central layer” that the central layer conducts electricityregardless of how it is implemented. Advantageously, the thickness ofthe electrically conductive flexible central layer is at least 15 μm.

In an advantageous embodiment, the thickness of the electricallyconductive flexible central layer lies in the range 20 μm to 40 μmapproximately, or better still in the range 25 μm to 35 μmapproximately, in particular approximately 30 μm.

In another advantageous embodiment of the invention, the thickness ofthe support layer lies in the range 10 μm to 15 μm approximately.Preferably, the support layer contains or is made of polyester.

In an advantageous embodiment, the support layer is metal plated over atleast one face that is to be arranged facing the electrically conductivecentral layer. Preferably, the metal plating of the support layer isimplemented using a metal or a metal alloy compatible with a metal ormetal alloy making the active central layer electrically conductive.

In a currently preferred embodiment, the electrically conductive activecentral layer contains or is constituted by at least one piece ofaluminum foil which may be about 30 μm thick. In which case, it iscurrently desirable for the metal plating of the support layer to beimplemented with a metal or a metal alloy chosen from silver, aluminum,or a combination of the two. The thickness of the metal plating is notcritical but its function is to provide a good link between the supportlayer and the active central layer. The thickness of the metal platingis generally about 1 μm or a few microns.

In another variant of the embodiment, the thickness of the “protective”layer may advantageously lie in the range 20 μm to 40 μm approximately,or better still in the range 20 μm to 30 μm approximately. Theprotective layer may contain or be made of polyester. In which case, thethickness of the protective layer is also about 25 μm.

According to another advantageous characteristic of the invention, thelayers are stuck together with an adhesive having a bonding force thatimparts sufficiently long-lasting mechanical strength to the multi-layerproduct for it to be unnecessary to change the multi-layer product whilethe element to be supported is on the support, in particular so as notto require a change to be made while a patient is being treated on abed. Preferably, the adhesive used must advantageously impart anadhesion capacity that makes it impossible to unstick the layers withouttearing them. Numerous adhesives having such a capacity are commerciallyavailable. An adhesive of the acrylic type is currently preferred.

In the context of the invention, it is also advantageous for theadhesive to be pre-applied, e.g. on one face of the active layer and onone face of the protective layer, so as to make the layers easier toassemble together.

In which case, the method of manufacturing the multi-layer product isparticularly simple, and it merely consists in gluing the active centrallayer as pre-provided with adhesive onto the support layer, and ingluing the protective layer having a face pre-provided with adhesiveonto the remaining other face of the active central layer by exerting abonding pressure dependent on the adhesive used, and by allowing theadhesive to take for a sufficient period of time, generally recommendedby the manufacturer of the adhesive. It is advantageous to use layershaving the dimensions required for the multi-layer product so as toavoid any subsequent cutting.

A multi-layer product is thus obtained that can constitute an inductivesensor element, and the multi-layer product can also be used toconstitute one of the elements of a measurement device for measuring thepenetration distance to which an element being supported, e.g. the bodyof a patient, penetrates into a support device, e.g. a mattress, thiscurrently constituting the preferred application of the invention.

In a second aspect, the present invention also provides an inductivesensor element, characterized in that it comprises a multi-layer filmproduct as defined above.

In a third aspect, the present invention also provides a measurementdevice for measuring the penetration depth to which an element beingsupported, in particular the body of a patient, penetrates into asupport device, e.g. a mattress or the like, in particular a supportdevice comprising at least one closed or controlled-release chamber thatis flexible and that is inflatable under an adjustable predeterminedinitial inflation pressure.

Advantageously, said chamber comprises a top face and a bottom face,said multi-layer film product being linked to the top face of saidchamber and a displacement distance measuring device being linked to thebottom face of said chamber.

In a fifth aspect, the present invention also provides a method and anapparatus for preventing or treating bedsores, comprising a multi-layerfilm product as defined above.

In the context of this fifth aspect, the present invention provides inparticular a support apparatus for supporting an element to besupported, in particular a patient P, comprising a measurement devicefor measuring the positioning of a supported element by a flexiblesupport device and a correlated deformation of said flexible supportdevice resulting from the action of said element to be supported actingon said support device in relationship with the volume and shape of saidsupported element, said measurement device comprising a flexible, supplesheet or film of a metallic thin foil, displaceable and deformable inspace submitted to a displacement and a deformation to be measured, inrelationship with the movement and the deformation of the flexiblesupport device, caused by said supported element, characterized in thatsaid flexible supple sheet or film of said metallic thin foil comprisesor is constituted of a multi-layer product as previously defined or asdefined in the following description in relationship with FIGS. 2 and 3.When the element to be supported is preferably a patient, the deformablesupport device is in general a mattress.

According to an advantageous invention feature, said deformable supportdevice further generally comprises at least one closed chamber inflatedor deflated by feeding in or releasing a fluid, for instance air,comprising an upper face and a lower face, said deformable flexiblesheet of a metallic thin foil being linked to the upper face of saidchamber and a measuring element, preferably an impedance varyingelement, being linked to the lower face of said chamber. Said impedancevarying element is preferably an induction coil.

According to a further particular advantageous invention embodiment,said apparatus further comprises control means acting on servo controlmeans for servo controlling the inflation pressure of said chamber tomaintain, while the element is being supported, a measured positionseparating the upper face from the lower face of said chamber preferablyat a predetermined distance value, for instance substantially constant,namely substantially equal to or within an acceptable variation, withrespect to a reference distance D_(c). Here, the position represents themeasured distance separating the closest point of the thin metallic foillinked to the upper face of the chamber, with respect to the lower face.

According to an advantageous variant embodiment, the control meanscomprise a control station comprising an electronic or electromechanicalcentral processing unit having a memory which unit continuously orintermittently receives signals that are proportional to the value ofthe measured position Dm, transmitted by the measurement device andcompares the measured values Dm with the reference distance value Dc,said control station further controlling servo control means for servocontrolling the inflation pressure of the chamber to obtain permanentlya measured position Dm essentially equal to the reference distance Dc orwithin an acceptable range of variation thereof.

According to a most preferred embodiment, the support device is abedsore mattress.

Other objects, characteristics and advantages of the invention willappear clearly on reading the following explanatory description madewith reference to two currently preferred embodiments of the inventiongiven by way of illustration and therefore in no way limiting the scopeof the invention. In the drawings:

FIG. 1 is a diagrammatic view of an embodiment of support apparatus asdescribed in FIG. 2 of the assignee's prior document: FR-A-2 718347=EP-A-0 676 158; which corresponds to U.S. Pat. No. 5,560,374; and

FIG. 2 shows the first embodiment of a multi-layer product of theinvention having an electrically conductive flexible active centrallayer, shown in dashed lines, e.g. usable for a support device having asingle chamber; and

FIG. 3 shows a second embodiment of a multi-layer product of theinvention, usable with a support element having at least one chamber.

FIG. 1 shows prior art support apparatus as described in Document FR-A-2718 347=EP-A-0 676 158, which corresponds to U.S. Pat. No. 5,560,374,and given the overall reference 10. This support apparatus makes itpossible to support an element, in particular the body of a patient P,as shown.

The apparatus 10 includes a support device proper 12, e.g. a mattress,comprising at least one closed or controlled-release chamber 14 that isflexible and inflatable. For example, the chamber may be composed of amultitude of inflatable tubes that communicate with one another, saidchamber 14 being inflatable under an adjustable predetermined initialinflation pressure. The chamber 14 has a top face 15 serving to supportthe element to be supported P, and a bottom face 16 which may, forexample, rest on a base (not shown) or on equivalent means. Theapparatus further includes servo-control means 18 for servo-controllingthe pressure at which the chamber 14 is filled as a function of thedistance to which the element being supported penetrates into thesupport device. For example, said servo-control means may comprisefilling means 20, such as pumping means 20 for pumping a filling fluidinto the chamber 14, such as a gas, in particular air, or a liquid, inparticular water, and they may include emptying means such as a valve22.

The apparatus also includes measurement means 30 for measuring thedistance D between the top face 15 of the chamber and its bottom face16.

The measurement means 30 may include a metal element 32, advantageouslyin the form of a piece of thin foil, secured to the top face 15 of thechamber 14, in this example inside said chamber 14, and cooperating withat least one inductive element 34 forming a position detector secured tothe bottom face 16 of said chamber 14, which inductive element may bearranged inside the chamber, integrated into the bottom face of thechamber 14, or else it may be secured to the outside of the bottom face16 of the chamber 14, as shown.

The apparatus also includes control means 40 that act on theservo-control means 18 for servo-controlling the inflation pressure ofthe chamber 14 to ensure that, while the element is being supported, thedistance D as measured between the top face 15 and the bottom face 16 ofthe chamber 14 is kept preferably at a predetermined distance value,e.g. an essentially constant value, i.e. a value essentially equal to areference distance D_(c), or within an acceptable range of variationthereabout.

The control means 40 may advantageously include a control station 42comprising an electronic or an electromechanical central processing unithaving a memory, which unit continuously or intermittently receivessignals that are proportional to the measured distance value D_(m) astransmitted by the above-mentioned measurement means 30, and comparesthe measured distance values D_(m) with the reference distance valueD_(c). The control station 42 controls the servo-control means 20, 22for servo-controlling the inflation pressure of the chamber 14 so that ameasured distance D_(m) is obtained that is essentially constantly equalto the reference distance D_(c) or within an acceptable range ofvariation thereabout.

The control means 40 are described in detail in the applicant's previousdocument FR-A-2 718 347=EP-A-0 676 158 in the description relating toFIGS. 1 to 4 and FIG. 6 thereof. EP-A-0 676 158 corresponds to U.S. Pat.No. 5,560,374, which is hereby incorporated by reference.

The control means 40 may include an oscillator device 44 which is shownin detail in FIG. 3 of FR-A-2 718 347=EP-A-0 676 158which corresponds toU.S. Pat. No. 5,560,374; and which is coupled to the inductive element34, such as an induction coil, an amplifier device 46 whose gain may beadjusted by a reference setting device 48 defining the referencedistance D_(c). The amplifier 46 is then coupled to aproportional-plus-integral, regulator device 50 coupled to a matchingdevice 52 whose output is coupled to the control station 42.

In the embodiment shown in FIG. 1, the inductive element 34, such as aninduction coil, is, for example, arranged on a reinforcing member 36positioned in the vicinity of that region of the element being supportedP which has the largest mass or which is most protuberant, namely thesacral region of the patient P in this example, as explained in theapplicant's above-mentioned prior document.

In the context of the applicant's prior document, the metal foil 32 hasa thickness of 10 μm, and is arranged between two insulating films so asto increase sensitivity, see page 9, lines 26 to 30 in FR-A-2 718 347,which corresponds to U.S. Pat. No. 5,560,374, which was satisfactory.

However, in the context of the present invention, the inventors setthemselves the technical problem of providing a solution making itpossible to avoid or to minimize perception of the presence of the metalfoil by an element being supported, in particular a patient.

Also in the context of the present invention, the inventors setthemselves the new technical problem of avoiding any physicaldisturbance that might be caused by the metal foil to the element beingsupported, in particular when the element is a patient undergoingtreatment.

Furthermore, in the context of the present invention, the inventors setthemselves the new technical problem of providing a solution making itpossible to make the metal foil very flexible, while greatly improvingits mechanical strength, and while also preventing it from deterioratingwhile it is operating.

All of these technical problems are solved for the first time in asimple, safe, and reliable way by the present invention, as illustratedby the two currently preferred embodiments of the invention describedwith reference respectively to FIGS. 2 and 3.

With reference to FIG. 2, the novel product of the invention concerns amulti-layer product given the overall reference 500. This multi-layerproduct 500 is characterized in that it comprises:

a flexible active central layer 532 which has the same function as themetal element 32 in the form of a piece of metal foil and described inthe applicant's prior document in particular with reference to FIGS. 1and 2; the active central layer 532 is therefore electricallyconductive, and, for example, it may be constituted by a piece of metalfoil which, in the context of the present invention, has a thickness ofat least 15 μm, defining two main faces of large area, as is easilyunderstandable since it is implemented in the form of a piece of foil,namely a first face glued onto at least one “support” layer 510 of anelectrically insulating synthetic material, shown larger in thisexample, and advantageously having a coefficient of elasticitysubstantially similar to the coefficient of elasticity of the activecentral layer 532, and a second face glued onto at least one“protective” second layer 520, in particular for protecting againstabrasion, and made of a an electrically insulating synthetic material,the total thickness of the multi-layer product being chosen so that theflexibility of the active central layer 532 is retained substantiallycompletely. Advantageously, the “protective” second layer also has acoefficient of elasticity that is substantially similar to that of theactive central layer 532.

Advantageously, the thickness of the active central layer 532 lies inthe range 20 μm to 40 μm approximately, or better still in the range 25μm to 35 μm approximately.

A currently preferred embodiment of the active central layer is a pieceof aluminum foil, in which case the currently ideal thickness is about30 μm.

In another advantageous variant of the invention, the thickness of thesupport layer 510 lies in the range 10 μm to 15 μm approximately.

In a currently preferred embodiment, the support layer 510 comprises oris made of polyester.

In another advantageous variant embodiment of the invention, the supportlayer 510 may be metal plated over at least one face that is to bearranged facing the central layer 532. The metal plating of the supportlayer 510 is advantageously implemented using a metal or a metal alloycompatible with the metal used to make the central layer 532electrically conductive. When the central layer 532 is made of aluminum,the support layer 510 is advantageously metal plated with a metal or ametal alloy chosen from silver and aluminum, or from a combination ofthe two.

In another advantageous variant embodiment of the invention, thethickness of the protective layer 520 lies in the range 20 μm to 40 μmapproximately, or better still in the range 20 μm to 30 μmapproximately.

In another advantageous variant embodiment, the protective layercomprises or is made of polyester, and its thickness is then currentlyideally about 25 μm.

According to another advantageous characteristic of the invention, theactive central layer 532 is glued to the support layer 510 and to theprotective layer 520 by means of an adhesive having a bonding force thatimparts high mechanical strength to the multi-layer product. Preferably,the adhesive has an adhesion capacity that makes it impossible tounstick the central layer 532 without tearing it. Numerous adhesives arecommercially available, and an adhesive of the acrylic type is currentlypreferred.

In an advantageous embodiment, the active central layer 532 ispre-provided with adhesive, as is the protective layer 520, therebyfacilitating gluing together the three layers, and manufacturing themulti-layer product.

For example, the size of the multi-layer product may be as follows: thesize of the central layer 532 may be 600 mm ×600 mm and it may beconstituted by a piece of aluminum foil that is about 30 μm thick; thesupport layer 510 may be made of polyester and have a size of 1,400 mm×975 mm, and a thickness of 13 ×m, the support layer being organized tobe positioned remote from the element being supported, such as the bodyof the patient, e.g. at the most suitable place along the supportelement 12 shown in FIG. 1, e.g. the region generally corresponding tothe sacral region; the protective layer 520, e.g. made of polyester, mayhave a size of 1,000 mm×700 mm, and a thickness of 25 μm, and beorganized so as to be positioned facing the element being supported,e.g. the body of a patient P in this example. Naturally, these sizes aregiven merely by way of illustration.

The multi-layer product may be combined with an adhesive tape 512 whichmakes it possible to secure the multi-layer product with the protectivelayer facing the element being supported, such as the body of a patientP, at the desired place along the support element 12 shown in FIG. 1.

The multi-layer product of the present invention can thus be used as aninductive sensor element having the function of the sensor 32 in themethod and apparatus described in the applicant's prior document withreference to FIG. 1; and it can also be used as one of the components ofa measurement device such as the measurement device 34 described in theassignee's prior document, and with reference to FIG. 1 and thereforefully applicable to the present invention.

A second embodiment of a multi-layer product of the present invention isshown in FIG. 3. The identical elements have the same reference numbersplus 100. For example, the flexible active central layer has thereference number 632, the support layer has the reference number 610,and the protective layer has the reference number 620. For example, theactive central layer 632 may be a piece of aluminum foil of size 600mm×600 mm and of thickness 30 μm, i.e. its dimensions are unchanged; thesupport layer 610 may be a layer of polyester e.g. about 13 μm thick andmetal plated over the face facing the metal layer 632 with silver, ofsize 1,100 mm×725 mm; and the protective layer 620 may be made ofpolyester, have a thickness of 25 μm, and a size of 1,000 mm×700 mm.Similarly, an adhesive tape 612 may be provided to bond the supportelement 12 to the multi-layer product 600 with the protective layer 620facing the element being supported, such as the body of a patient P.

By means of the multi-layer product of the present invention, all of theabove-mentioned technical problems are solved. In particular, the activecentral layer is protected well. Furthermore, the patient generally nolonger notices the existence of the metal element forming the inductionsensor. The flexibility of the multi-layer product enables it to fitperfectly the morphology of the element being supported, in particularthe body of a patient. The multi-layer product is thus very flexible andvery strong mechanically, in particular it has very good resistance todeterioration while it is operating. There is almost no possibility ofthe multi-layer product being delaminated while it is in normal use,thereby removing any risk of abrasion or deterioration of the activeportion. Furthermore, by means of the metal plating of the supportlayer, expected behavior is obtained from the inductive sensor elementwith a better electromagnetic compatibility in terms of radiationimmunity.

The invention thus offers a decisive advantage in the context ofmeasurement devices for measuring the penetration depth to which anelement being supported, such as the body of a patient P, penetratesinto a support element 12, such as a mattress having at least oneflexible chamber inflatable to an adjustable predetermined inflationpressure, as a person skilled in the art can well understand from thedescription of the present invention, and with reference to theapplicant's previous document FR-A-2 718 347=EP-A-676 158, whichcorresponds to U.S. No. 5,560,374.

Naturally, the invention covers any characteristic which appears to benovel compared with any state of the art. Furthermore, the inventioncovers any means constituting techniques that are equivalent to themeans described and shown. In addition, FIGS. 2 and 3 form an integralpart of the present invention and therefore of the present description.

What is claimed is:
 1. An apparatus for supporting a patient having aposition measuring device, including an impedance varying element and amultilayer, flexible film of a thin metal foil movable and deformable inspace that cooperates with said impedance varying element, said flexiblefilm comprising: an electrically conductive, flexible, active, centrallayer having a coefficient of elasticity, a flexibility, and two mainfaces of large area, a first face and a second face; at least onesupport layer formed of a synthetic material that is electricallyinsulating, and that has a coefficient of elasticity substantiallysimilar to the coefficient of elasticity of the active central layer,the support layer being linked to the first face of the central layer;and at least one protective second layer, formed of an electricallyinsulating synthetic material, the second layer being linked to thesecond face of the central layer, the total thickness of the multi-layerfilm being predetermined to retain substantially completely theflexibility of the central layer.
 2. The apparatus according to claim 1,wherein a thickness of the central layer is between about 10 μm and 40μm.
 3. The apparatus according to claim 1, wherein a thickness of thesupport layer is between about 10 μm and 15 μm.
 4. The apparatusaccording to claim 1, wherein the support layer comprises polyester. 5.The apparatus according to claim 1, wherein the support layer comprisesmetal plating over at least one face of the support layer facing thecentral layer.
 6. The apparatus according to claim 5, wherein the metalplating of the support layer comprises a metal or a metal alloycompatible with a metal of the central layer.
 7. The apparatus accordingto claim 5, wherein the central layer comprises a flexible film of foilmade of aluminum or of an aluminum alloy, and the metal plating of thesupport layer comprises a metal or a metal alloy selected from the groupconsisting of silver, aluminum and a combination of silver and aluminum.8. The apparatus according to claim 1, wherein a thickness of theprotective second layer is between about 20 μm and 40 μm.
 9. Theapparatus according to claim 1, wherein the protective layer comprisespolyester.
 10. The apparatus according to claim 1, wherein said centrallayer is linked with said support layer and said protective layer by anadhesive having a bonding force of a high mechanical strength and anadhesion capacity that impedes unsticking of the multi-layer productwithout tearing the central layer.
 11. The apparatus according to claim10, wherein said adhesive is an acrylic adhesive.
 12. The apparatusaccording to claim 1, wherein said supporting apparatus comprises amattress having at least one closed chamber inflatable with a fluid,said chamber having a top face and a bottom face, said flexible filmbeing linked to the top face of said chamber, and cooperating with saidat least one impedance varying element linked to the bottom face of saidchamber, and wherein said supporting apparatus further comprises controlmeans acting on servo control means for servo controlling an inflationpressure of said chamber to maintain at a predetermined value, whilesupporting a patient, a distance from a closest point on the top face tothe bottom face of the chamber.
 13. The apparatus of claim 12, whereinsaid control means comprise a control station comprising a centralprocessing unit having a memory, the central processing unitcontinuously or intermittently receiving signals proportional to thevalue of the position of the closest point between the top face and thebottom face, as transmitted by the measuring device and comparing thevalues of the distance of the closest point from the bottom face with areference value, said control station controlling the means for servocontrolling the inflation pressure of the chamber to obtain a distancebetween the closest point of the top face from the bottom faceessentially constantly equal to the reference value.
 14. The apparatusaccording to claim 1 wherein the central layer includes a thin metalfoil.
 15. A method of treating a bedsore or preventing or lowering arisk of occurrence of a bedsore of a patient lying on a mattress, saidmethod comprising: providing a mattress comprising at least one closedor controlled release chamber, said chamber being flexible andinflatable at an adjustable, predetermined initial inflation pressure,said chamber having a top face for supporting a patient and a bottomface; providing a measurement device comprising a flexible film linkedto the top face of said chamber and cooperating with at least oneimpedance varying element linked to the bottom face of said chamber,said flexible film comprising; an electrically conductive, activecentral layer having a coefficient of elasticity, a flexibility and twomain faces of large area, a first face and a second face; at least onesupport layer of a synthetic material that is electrically insulating,and that has a coefficient of elasticity substantially similar to thecoefficient of elasticity of the active central layer, said supportlayer being linked to the first face of said central layer; and at leastone protective second layer made of an electrically insulating syntheticmaterial, the protective layer being linked to the second face of saidcentral layer, a total thickness of the film being predetermined tosubstantially retain the flexibility of the central layer; andmaintaining a distance of a closest point on the flexible film from thebottom face of the chamber at a predetermined value which issubstantially equal to a reference distance.
 16. The method of claim 15,further comprising providing control means and servo control means, saidcontrol means acting on said servo control means for servo controllingan inflation pressure of the chamber to maintain the distance of theclosest point on the flexible film from the bottom face of the chamberat the reference distance while a patient is supported on said mattress.17. The method of claim 16, wherein said control means further comprisea control station comprising a central processing unit having a memory,the central processing unit continuously or intermittently receivingsignals proportional to the value of the distance of the closest pointon the foil from the bottom face of the chamber transmitted by saidmeasurement device and comparing the distance of the closest point onthe foil from the bottom face with the reference distance.
 18. Themethod of claim 15, wherein a thickness of the central layer is betweenabout 15 μm and 40 μm.
 19. The method of claim 15, wherein a thicknessof the support layer is between about 10 μm and 15 μm.
 20. The method ofclaim 15, wherein the support layer comprises polyester.
 21. The methodof claim 15, wherein the support layer comprises metal plating on atleast one face facing the central layer.
 22. The method of claim 21,wherein the metal plating of the support layer comprises a metal or ametal alloy compatible with a metal of the central layer.
 23. The methodof claim 15, wherein the central layer comprises a flexible film of foilmade of aluminum or of an aluminum alloy, and the support layercomprises a metal plating formed of a metal or a metal alloy selectedfrom the group consisting of silver, aluminum and a combination ofsilver and aluminum.
 24. The method of claim 15, wherein a thickness ofthe protective layer is between about 20 μm and 40 μm.
 25. The method ofclaim 15, wherein the protective layer comprises polyester.
 26. Themethod of claim 18, wherein said central layer is linked with saidsupport layer and said protective layer with an adhesive having abonding force of a high mechanical strength and an adhesion capacitythat impedes unsticking of the multi-layer product without tearing thecentral layer.
 27. The method of claim 26, wherein said adhesive is anacrylic adhesive.
 28. The method of claim 15, wherein the central layerincludes a thin metal foil.
 29. A flexible film movable and deformablein space, said flexible film, comprising: an electrically conductive,flexible, active central layer having a coefficient of elasticity, aflexibility, and two main faces of large area, a first face and a secondface; at least one support layer of a synthetic material that iselectrically insulating, and that has a coefficient of elasticitysubstantially similar to the coefficient of elasticity of the centrallayer, the support layer being linked to the first face of the centrallayer; and at least one protective second layer made of an electricallyinsulating synthetic material, the second layer being linked to thesecond face of the central layer, the total thickness of the film beingpredetermined to retain substantially completely the flexibility of theactive central layer, said central layer being of a size smaller than asize of the support layer and a size of the protective layer.
 30. Theflexible film of claim 29, wherein the size of the central layer isabout 600 mm by 600 mm and the size of the support layer is about 1,100mm to 1,400 mm by 725 mm to 915 mm and the size of the protective layeris about 1,000 mm by 700 mm.
 31. The film of claim 29, wherein athickness of the central layer is between about 15 μm and 40 μm.
 32. Thefilm of claim 29, wherein the thickness of the support layer is betweenabout 10 μm and 15 μm.
 33. The film of claim 29, wherein the supportlayer comprises polyester.
 34. The film of claim 29, wherein the supportlayer comprises a metal plating over at least one face facing thecentral layer.
 35. The film of claim 34, wherein the metal plating ofthe support layer comprises a metal or a metal alloy compatible with ametal of the central layer.
 36. The film of claim 29, wherein thecentral layer comprises a flexible film of foil made of aluminum or ofan aluminum alloy, and the support layer comprises a plating of a metalor a metal alloy selected from the group consisting of silver, aluminumand a combination of silver and aluminum.
 37. The film of claim 29,wherein a thickness of the protective layer is between about 20 μm and40 μm.
 38. The film of claim 29, wherein the protective layer comprisespolyester.
 39. The film of claim 29, wherein said central layer islinked with said support layer and said protective layer with anadhesive having a bonding force of a high mechanical strength and anadhesion capacity that impedes unsticking of the multi-layer productwithout tearing the central layer.
 40. The film of claim 39, whereinsaid adhesive is an acrylic adhesive.
 41. The flexible film of claim 29wherein the central layer includes a thin metal foil.